A native of Wakanda, he was born under the name N'Jadaka. When Ulysses Klaw and his mercenaries attacked Wakanda, they press-ganged N'Jadaka's father into helping them; when Klaw was defeated, the father died and his family was exiled. N'Jadaka ended up in Harlem, New York, nursing a hatred against the supervillain and T'Challa, the king who'd exiled him. He changed his name to Erik Killmonger and studied at MIT, desperate to avenge his father's death.
He eventually contacted King T'Challa and was repatriated back to Wakanda, settling in a village that would later change its name to N'Jadaka Village in his honour. He became a subversive, with dreams of ridding Wakanda of what he termed "white colonialist" cultural influences and return it entirely to its ancient ways. He then took advantage of the Black Panther's frequent absences in America with the Avengers to stage a coup d'etat, along with Baron Macabre. He was defeated and killed[1], until the Mandarin claimed his body.[2].
Using his rings, the Mandarin was able to amplify the Resurrection Altar and restore him to life. Killmonger returned to his lover and ally, Madam Slay and the two plotted to kill the Black Panther and return Wakanda to its ancient ways.
While Tony Stark visited Wakanda, Madam Slay drugged Jim Rhodes and took him prisoner. Killmonger appeared to have killed the Black Panther, and blamed Rhodes and Stark, convincing the Wakandans that he could lead them to vengeance. The Black Panther returned, revealing that he had faked his death using an LMD. The Black Panther defeated Killmonger. The Mandarin recalled his ring, and Killmonger reverted to an inanimate skeleton.
Killmonger's followers resurrected him again and he would clash with T'Challa on several other occasions.
In the wake of the sorcerer Reverend Achebe's attempted takeover of Wakanda, with T'Challa absent and control of the country left with his regent Everett Ross, Killmonger tried to gain control of the country via its economy, forcing T'Challa to stop him by nationalizing all foreign companies in Wakanda and cause a run on the stock market. The two foes fought in a vicious ritual combat over the right to rule the country, and Killmonger was finally able to defeat his foe and gain the status of Black Panther for his own. He maintained control of Wakanda for a while and even attempted to inherit T'Challa's Avengers status, but when he underwent the ascension rite needed to cement his position, his body had a severe reaction to the heart-shaped herb that he was required to consume - it was poisonous to all but the royal bloodline. Although it would have been convenient to allow him to die, and be unquestionably entitled to the position of the Black Panther, T'Challa preserved his rival's life.
Killmonger eventually came out of his coma, thus reclaiming his position as chieftain over Wakanda. He went to New York and contacted Kasper Cole, an inner-city police officer masquerading as the Black Panther to help him with cases, and attempted to gain him as an ally (and one-up T'Challa) by offering him a buffered version of the Panther's heart-shaped herb and help finding his supervisor's kidnapped son. In exchange, he had to drop the Panther identity and take up that of a White Tiger acolyte of the Panther cult, and would owe Killmonger a favor. While Kasper agreed to this, he then used his new herb-enhanced abilities to track down the boy on his own to avoid owing Killmonger an unpayable debt.
Killmonger has not yet been seen in the fourth Black Panther solo series and T'Challa is once again the solo ruler of Wakanda; presumably he was able to successfully challenge Killmonger's right to rule between the third and fourth volumes.